This section provides background information to facilitate a better understanding of various aspects of the invention. It should be understood that the statements in this section are to be read in this light, and not as admissions of prior art.
The invention relates in general to downhole (e.g., subsurface, subterranean) wellbore operations and, more specifically, to methods and apparatus for operating multiple, e.g., 2 or more, downhole hydraulic tools utilizing a minimal number of hydraulic lines.
To meet the increasing need for hydrocarbons, wells (e.g., subterranean wellbores) are being drilled deeper and in more hostile downhole environments. In many instances a single wellbore can penetrate multiple geological formations, or zones, from which fluid may be produced or injected. Often a large number of controllable downhole tools are required to realize the potential of these wells. The challenge of controlling downhole tools increases with the number of downhole tools utilized and the hostile wellbore environment. For example, electrical control systems are often unreliable and/or short-lived. High downhole temperatures often limit electrical control systems. The wellbore fluids, for example drilling fluids (“mud”) and completion fluids, are often highly electrolytic and can adversely affect exposed electric circuits. Corrosive fluids in the well, such as hydrogen sulfide and carbon dioxide, attack electrical connections, conductors and insulators.
It has become common to deploy hydraulic control lines in subterranean wellbores to control the downhole tools. Packers, valves, and perforating guns are some of the downhole tool types that can be controlled by changes in pressure in the fluid contained in the hydraulic control lines. Typically the top end of each control line extends to the surface (land or sea floor) and is connected to a hydraulic pump that can control the pressure of the fluid inside the line. A control line must be passed through a feedthrough of a packer in order to extend the control line from the top to the bottom of the packer (or across the packer). Among others, a function of a packer is to seal the wellbore annulus across the packer. However, each time a control line is extended through a feedthrough, a potential leak path is created in the packer potentially allowing the seal created by the packer to fail. Still further, the limited space or pre-existing equipment in the wellbore may limit the number of hydraulic control lines and thus the number of controllable downhole tools that may be utilized.
Therefore, there is a continuing desire for hydraulic control methods and apparatus that provide for control of a multiplicity of downhole tools with a minimum number of hydraulic control lines from the surface. There is a still further desire for hydraulic control methods and apparatus that provide operational complexity of electric control systems, with only a few hydraulic inputs by use of hydraulic fluid flow, hydraulic fluid pressure oscillation, and hydraulic fluid pressure.